The present invention relates to air atomizing spray guns, and in particular to an improved air atomizing spray gun which accommodates selective control over atomizing and fan-shaping air emitted from the gun.
As is known, air atomizing spray guns have a circular fluid outlet orifice from which a cylindrical stream of liquid coating material or paint is emitted. Circumferentially surrounding the fluid orifice is an annular orifice through which atomizing air flows for interaction with the fluid stream to mechanically atomize it into an expanding, conically-shaped spray. Although articles may be coated with a conically-shaped spray, for uniformity of coating application it is usually desirable that the spray be fan-shaped. Therefore, such spray guns customarily also have means for impinging jets of air against opposite sides of the conically-shaped spray to form or flatten it to a fan shape.
Conventionally, air spray guns have a single air inlet for receiving air under pressure and directing it through passages to the atomizing air orifice, and a valve for diverting a portion of the air to the fan-shaping air orifices. A disadvantage is that for a given pressure of air supplied to the gun, the greater the amount of fan air required to form a properly shaped spray pattern, the less air will be available for atomization purposes.
It is desirable that an air spray gun emit the least amount of air necessary for proper atomization and fan-shaping, whereby to minimize air supply requirements as well as overspray and bounceback. Low solids coating materials, i.e., those having a relatively low ratio of pigment to solvent, require less air to atomize than high solids coating materials, so with low solids materials increases in fan-shaping air can usually be made without adversely affecting atomization quality. However, when spraying high solids materials, it often is not possible to increase fan air at the expense of atomizing air without impairing the quality of atomization. Although the pressure of air supplied to the gun may be adjusted to accommodate satisfactory atomizing and fan air flow rates while maintaining an overall minimum level of air emission from the gun, the expedient is inconvenient, since the air pressure regulator is usually at a position remote from the gun.